The present invention relates to a combined oil ring assembly which has an expander improved with fatigue resistance. The combined oil ring assembly or oil control piston ring includes the expander and side rails seated on upper and lower surfaces of the expander, which is fitted into the groove of a reciprocating piston primarily employed in internal combustion engines. The outer peripheral edges of the side rails will contact the inner wall of the cylinder and prevent leakage of oil due to a spring-like property of the expander.